Composite material-stiffened panel and manufacturing method thereof

ABSTRACT

A composite material-stiffened panel has a skin obtained by molding a fiber-reinforced resin composite material into a flat skin, stiffeners arranged in rows on one surface of the skin, and a fiber-reinforced resin-composite material stitched on the skin covering the stiffeners. The composite material-stiffened panel can be manufactured as follows: A first fabric material is placed on a tool having a panel-shaped surface. Stiffeners are placed on the first fabric materials. A second fabric material is placed on the stiffeners to cover at least some of the stiffeners. The second fabric materials are reformed to match the shape of the stiffeners. The reformed second fabric material is stitched on the first fabric material along edges of the stiffeners. All the materials are covered with a bagging film for vacuum. Resin is infiltrated into the fabric materials by a RTM or a RFI method. The infiltrated resin is heated to be hardened.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a composite material-stiffened panel tobe applied to a wing and a tail assembly of an aircraft and amanufacturing method thereof.

2. Description of the Related Art

As a conventional stiffened panel, stiffened panels shown in FIGS. 1through 4 are known.

A stiffened panel 10 shown in FIG. 1 is formed in such a manner that askin 11 and a stiffener 12 are manufactured according to respectiveshapes, and they are bound to each other by a fastener 13 (rivet or thelike).

A stiffened panel 10 a shown in FIG. 2 is formed in such a manner that askin 11 a and a stiffener 12 a are manufactured according to respectiveshapes, and they are bonded by an adhesive 14.

A stiffened panel 10 b shown in FIG. 3 is formed in such a manner that ametal thick plate 15 shown by a dotted line is machined to be astiffened panel (solid line).

A stiffened panel 10 c shown in FIG. 4 is formed in such a manner that acomposite material is formed into a stiffened plate by molding a skin 17and a stiffener 18 integrally by means of a molding tool 16.

The method of manufacturing a stiffened panel by binding a skin and astiffener by means of a fastener requires molding of the skin and thestiffener and provision of a positioning tool, thus resulting in highcost. Other problems are strict fastener design requirements (hole-edgedistance and skin thickness for no sharp edges to a countersink) andreducing of fatigue strength due to a fastener-hole stressconcentration.

The method of manufacturing a stiffened panel by bonding a skin and astiffener by means of an adhesive requires molding of the skin and thestiffener, a pre-bonding process for the skin and the stiffener,positioning the skin and the stiffener, and provision of a pressurizedholding tool for bonding, thus the cost becomes high.

The method of manufacturing a stiffened panel by machining a thick metalplate by machine working has a problem that since much of the materialis cut and discarded, resources are wasted, and a problem that as weightefficiency is heightened, the cost of machine working becomes higher.

The method of manufacturing a stiffened panel by means of integralmolding of a composite material has a problem of high cost factors suchas provision of a complex tool for an accurately and integrally moldedshape and of pressurizing the entire surface and an increase in scraprisk.

SUMMARY OF THE INVENTION

In view of the problems discussed above, an object of the presentinvention is to provide a composite material-stiffened panel forenhanced bonding of a fiber-reinforced resin-composite skin and astiffener and a manufacturing method thereof.

The present invention provides a composite material-stiffened panelincluding: a skin obtained by molding a fiber-reinforced resin-compositematerial into a flat skin; stiffeners arranged in rows on one surface ofthe skin; and a fiber-reinforced resin-composite material stitched onthe skin and covering the stiffeners.

Moreover, the present invention provides a method of manufacturing acomposite material-stiffened panel including the steps of: placing afirst fabric material on a tool having a panel-shaped surface; placingstiffeners on the first fabric material; placing a second fabricmaterial on the stiffeners so as to cover at least some of thestiffeners; reforming the second fabric material so as to match theshape of the stiffeners; stitching the reformed second fabric materialon the first fabric material along edges of the stiffeners; covering allthe materials with a bagging film for vacuum; infiltrating resin intothe fabric materials by a RTM or a RFI method; and heating theinfiltrated resin to be hardened.

Moreover, the present invention provides a method of manufacturing acomposite material-stiffened panel including the steps of: placing afirst fabric material on a tool having panel-shaped surface; placing asecond fabric material on the first fabric material so as to be loosenedin some places for stiffeners to be put through; putting the stiffenersthrough between the loosened second fabric material and the first fabricmaterial; reforming the second fabric material so as to match the shapeof the stiffeners; stitching the reformed second fabric material on thefirst fabric material along edges of the stiffeners; covering all thematerials with a bagging film for vacuum; infiltrating resin into thefirst and second fabric materials by a RTM or a RFI method; and heatingthe infiltrated resin, to be hardened.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an illustration showing a conventional in stiffened panel;

FIG. 2 is an illustration showing another conventional stiffened panel;

FIG. 3 is an illustration showing still another conventional stiffenedpanel;

FIG. 4 is an illustration showing a further conventional stiffenedpanel;

FIG. 5 is a perspective view showing an embodiment of a compositematerial-stiffened panel according to the present invention;

FIG. 6 is an illustration showing one example of a method of attaching amolded rib to a skin;

FIG. 7 is an illustration showing another example of a method ofattaching a molded rib to a skin;

FIG. 8 is an enlarged section showing the composite material-stiffenedpanel of the present invention; and

FIG. 9 is a perspective view showing another embodiment of a compositematerial-stiffened panel according to the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Preferred embodiments according to the present invention will bedisclosed with reference to the attached drawings.

In FIG. 5, a composite material-stiffened panel 1 is applied to anaircraft wing and tail-assembly to be a fuel tank.

The composite material-stiffened panel 1 has a skin 2, severalstiffeners 3, a fiber-reinforced resin-composite material 4 and ribs 5.The skin 2 is obtained by molding a fiber-reinforced resin-compositematerial into a flat skin. The stiffeners 3 are arranged in rows on onesurface of the skin 2 with a gap in one direction. The fiber-reinforcedresin-composite material 4 is provided on and stitched on the skin 2 soas to partially cover the stiffeners 3. The ribs 5 connect thestiffeners 3 each arranged in rows.

It is preferable that the fiber of the fiber-reinforced resin-compositematerial 2 is composed of a composite-material dry preform ofthree-dimensional fabric where warp, weft and vertical yarn are combinedthree-dimensionally with warp-enhanced inter-layer strength in athickness-wise direction. The fiber of the fiber-reinforcedresin-composite material 2 may, however, be obtained by laminating andstitching integrally normal fabrics.

Each stiffener 3 is made of a composite material having an approximatelyU-shaped section with a flange portion extended outward. The compositematerial is hardened or semi-hardened for molding. As for the shape,even if the stiffener 3 is not formed in accordance with a moldedcontact individually, they preferably have shape characteristic thattheir open cross section has twist and bending flexibility and onlyaxial rigidity is sufficient. It is also preferable that the stiffener 3has a shape such that it is rigid in an axial direction and it istwisted and bent sufficiently, for example, has an open cross section oflike a thin channel material.

In the present embodiment, each stiffener 3 is a fiber-reinforcedresin-composite material, but it may be a metal member. For example,when the composite material is a carbon fiber-reinforced resin-compositematerial, a surface-treated titanic alloy can be used as the stiffener3.

It is preferable that the fiber of the fiber-reinforced resin-compositematerial 4 is a three-dimensional fabric where warp, weft and verticalyarn in three direction are combined three-dimensionally. The fiber ofthe fiber-reinforced resin-composite material 4 may, however, beobtained by laminating and stitching integrally several normal fabrics.

As shown in FIG. 6, the rib 5 is formed in such a manner that a portionof one end of a prepreg-band material through which the stiffener 3 isto be put is cut out and is bent by a molding tool 7 so as to have anL-shaped section. Moreover, as shown in FIG. 7, the rib 5 may be formedin such a manner that two prepregs are molded by the molding tool 7 soas to have a L-shaped section for lamination. The rib 5 is placed on theskin 2 via an adhesive 8 and is heated to be hardened together with theskin 2, the stiffener 3 and the fiber-reinforced resin-compositematerial 4 for bonding.

In FIG. 8, a stitch yarn 9 is used for binding the skin 2 and thefiber-reinforced resin-composite material 4.

A method of manufacturing a composite material stiffened panel will beexplained below.

In this explanation, the same reference numerals are given to thefiber-reinforced resin-composite material and fiber composing it in thecommon portions.

Prepared first are a three-dimensional fabric material 2 whichreinforces the skin 2, the stiffener 3 made of a hardened orsemi-hardened fiber-reinforced resin-composite material, anotherthree-dimensional fabric materials 3 which reinforce thefiber-reinforced resin-composite material 4, and a prepreg rib 5 moldedto have a L-shaped section.

The three-dimensional fabric material 2 is placed on a molding surfaceof a tool (not shown) having a panel-shaped surface. The stiffeners 3are arranged in rows on the three-dimensional fabric material 2 with aninterval in one direction.

The other three-dimensional fabric material 4 is placed on thethree-dimensional fabric material 2 so as to cover the stiffeners 3 sothat it crosses over from one side to the other side. The otherthree-dimensional fabric material 4 may, however, cover some stiffeners3.

The other three-dimensional fabric material 4 placed to cover thestiffeners 3 is reformed to match the shape of the outer surface of eachstiffener 3.

The reformed other three-dimensional fabric material 4 is subject to astitching process along edge portions of the stiffeners 3 in alongitudinal direction of the stiffeners 3. The other three-dimensionalfabric material 4 is bound to the three-dimensional fabric material 2 bya stitch yarn 9. As a result, the stiffeners 3 can be positioned onpredetermined positions without a positioning tool.

The ribs 5 of band-shaped prepreg with a molding tool 7 abutting onportions from which the arranged stiffeners 3 have been removed areplaced on the three-dimensional fabric material 2 or 4 via the adhesive8 (in FIG. 5, the molding tool is omitted).

All of the materials are covered with a bagging film for vacuum (notshown). Resin is introduced into the fabric materials by a RTM (resintransfer molding) method or a RFI (resin film infusion) method. Theinfiltrated resin is then heated to be hardened to mold the compositematerial-stiffened panel 1.

FIG. 9 shows another embodiment of a method of manufacturing thecomposite material-stiffened panel 1 according to the present invention.

In FIG. 9, elements in this embodiment that are identical or analogousto the elements in the former embodiments are referenced by the samenumerals.

Prepared first are the three-dimensional fabric material 2, thestiffeners 3 made of hardened or semi-hardened fiber-reinforcedresin-composite material, the other three-dimensional fabric material 4,the ribs 5 where one end of a band-shaped prepreg has been partiallynotched and bent to provide a bent L-shaped section, and the moldingtool 7.

The three-dimensional fabric material 2 is placed on a molding surfaceof a tool (not shown) having a panel-shaped surface. The band-shapedfabric material 4 is placed on the three-dimensional fabric material 2so as to be loosened in some places so that the stiffeners 3 can be putthrough. A width of the other fabric material 4 may be such that itcovers all of the stiffeners 3 or covers some of them.

The stiffeners 3 are put between the loosened fabric material 4 and thefabric material 2. Portions of the loosened fabric material 4corresponding to edges of the stiffeners 3 are stitched so that theother three-dimensional fabric material 4 is bound to thethree-dimensional fabric material 2 by the stitch yarn 9. As a result, apositioning tool for the stiffeners for hardening is not necessary.

The ribs 5 are placed on the other fabric material 4 via the adhesive 8with the molding tool 7 on which the ribs 5 are abutting while avoidingthe notches of the stiffeners 3 arranged in rows (in FIG. 5, the moldingtool 7 is omitted).

All of the materials are covered with a bagging film for vacuum, andresin is infiltrated into the fabric materials by the RTM or the RFImethod, and the infiltrated resin is heated to be hardened to form thecomposite material-stiffened panel 1.

According to the composite material-stiffened panel of the presentinvention, the stiffeners arranged on the skin made of thefabric-reinforced resin-composite material is covered with anotherfabric-reinforced resin-composite material stitched on the skin alongthe edges of the stiffeners, so that the joint strength of thestiffeners and the skin is improved.

In the composite material stiffened panel manufacturing method of thepresent invention, the fabric material is placed on a tool having apanel-shaped surface and the stiffeners are placed thereon. Anotherfabric material is placed on the stiffeners so as to cover at least someof the stiffeners, the fabric material being reformed to match the shapeof the stiffeners. The reformed fabric material is stitched on thefabric material along the edges of the stiffeners. All of the materialsare covered with the bagging film for vacuum. Resin is infiltrated intothe fabric materials by the RTM or the RFI method, and the infiltratedresin is heated to be hardened. As a result, it is not necessary topreviously mold stiffeners one by one. The stiffeners can be positionedeasily by stitching. Moreover, manufacturing of several molding toolsand their complicated attachment and removal works can be omitted.

Furthermore in the composite material-stiffened panel manufacturingmethod of the present invention, the fabric material is placed on thetool having a panel-shaped surface. Another fabric material is placed onthe aforementioned fabric material so that it is loosened in some placesfor the stiffeners to be put through. The stiffeners are put throughbetween the loosened fabric material and the fabric material. Portionsof the loosened fabric material corresponding to the edges of thestiffeners are stitched. All of the materials are covered with thebagging film for vacuum. Resin is infiltrated into the fabric materialsby the RTM or the RFI method, and the infiltrated resin is heated to behardened. As a result, it is not necessary to previously mold stiffenersone by one. The stiffeners can be positioned easily by stitching.Moreover, manufacturing of several molding tool and their complicatedattachment and removal works can be omitted.

What is claimed is:
 1. A composite material-stiffened panel manufacturing method comprising the steps of: placing a first fabric material on a tool having a panel-shaped surface; placing stiffeners on said first fabric material; placing a second fabric material on the stiffeners so as to cover at least some of said stiffeners; reforming said second fabric material so as to match the shape of said stiffeners; stitching said reformed second fabric material on said first fabric material along edges of said stiffeners; covering all the materials with a bagging film for vacuum; infiltrating resin into said fabric materials by a RTM or a RFI method; and heating the infiltrated resin to be hardened.
 2. The composite material-stiffened panel manufacturing method according to claim 1, wherein said first and second fabric materials are stitched after three-dimensional fabrics or fabrics are laminated.
 3. The composite material-stiffened panel manufacturing method according to claim 1, wherein after said reformed second fabric material has been stitched on said first fabric material along the edges of said stiffeners, prepreg ribs are arranged on said first fabric material and said stiffeners or said second fabric material so as to cross said stiffeners and to abut on a molding tool, all the materials including the molding tool are covered with the bagging film for vacuum, the resin is infiltrated into said first and second fabric materials by the RTM or the RFI method, and the infiltrated resin is heated to be hardened.
 4. The composite material-stiffened panel manufacturing method according to claim 1, wherein said reformed second fabric material is subject to a stitching process along edge portions of said stiffeners in a longitudinal direction of said stiffeners.
 5. The composite material-stiffened panel manufacturing method of claim 1, wherein the stiffeners placed on said first fabric material are made of a fiber-reinforced resin-composite material.
 6. The composite material-stiffened panel manufacturing method of claim 1, wherein the stiffeners placed on said first fabric material have open cross-sections defining longitudinally extending hollow channels.
 7. The composite material-stiffened panel manufacturing method of claim 1, wherein said stiffeners have a U-shaped cross-section with a central raised portion and flange portions extending outwardly to opposite sides of said central raised portion.
 8. The composite material-stiffened panel manufacturing method of claim 1, wherein said stiffeners placed on said first fabric material are of metal.
 9. The composite material-stiffened panel manufacturing method of claim 1, further comprising adhering ribs with an L-shaped cross-section to said first fabric material.
 10. The composite material-stiffened panel manufacturing method of claim 1, wherein pairs of L-shaped ribs are arranged back-to-back along said first fabric material.
 11. The composite material-stiffened panel manufacturing method of claim 1, further comprising positioning said stiffeners on said first fabric material by extending stitch lines in a direction of elongation of said stiffeners and to opposite side edges of each of said stiffeners to align said stiffeners without a need for a positioning tool.
 12. A composite material-stiffened panel manufacturing method, comprising the steps of: placing a first fabric material on a tool having panel-shaped surface; placing a second fabric material on said first fabric material so as to be loosened in some places for stiffeners to be put through; putting the stiffeners through between said loosened second fabric material and said first fabric material; reforming said second fabric material so as to match the shape of said stiffeners; stitching said reformed second fabric material on said first fabric material along edges of said stiffeners; covering all the materials with a bagging film for vacuum; infiltrating resin into said first and second fabric materials by a RTM or a RFI method; and heating the infiltrated resin to be hardened.
 13. The composite material-stiffened panel manufacturing method according to claim 12, wherein said first and second fabric materials are stitched after three-dimensional fabrics or fabrics are laminated.
 14. The composite material-stiffened panel manufacturing method according to claim 12, wherein after said reformed second fabric material has been stitched on said first fabric material along the edges of said stiffeners, prepreg ribs are arranged on said first fabric material and said stiffeners or said second fabric material so as to cross said stiffeners and to abut on a molding tool, all the materials including the molding tool are covered with the bagging film for vacuum, the resin is infiltrated into said first and second fabric materials by the RTM or the RFI method, and the infiltrated resin is heated to be hardened.
 15. The composite material-stiffened panel manufacturing method according to claim 12, wherein said reformed second fabric material is subject to a stitching process along edge portions of said stiffeners in a longitudinal direction of said stiffeners.
 16. A composite material-stiffened panel manufacturing method comprising the steps of: placing a first fabric material on a tool; placing stiffeners on said first fabric material; placing a second fabric material on the stiffeners so as to cover at least some of said stiffeners; positioning said stiffeners on said first fabric material by extending stitch lines in a stitching direction that corresponds with a direction of elongation of said stiffeners and to opposite side edge of said stiffeners, and said extending of stitch lines involves stitching said reformed second fabric material to said first fabric material; subjecting the first and second fabric materials and stiffeners to a vacuum process; infiltrating resin into said fabric materials by a RTM or a RFI method; and heating the infiltrated resin to be hardened. 